Scanning acoustic microscope for mechanical characterization and density estimation of irradiated nuclear fuel

• An acoustic microscope from Montpellier University was introduced in ITU hot cells.
• Young's modulus of fuel pellets is assessed in a non destructive and local way.
• Fuel density is estimated in a few minutes with an acceptable precision.
• Behaviour laws are proposed from 0 to 103 MWd kg−1.

Thanks to high frequency ultrasonic surface waves generated by specific focused transducers, a non destructive evaluation of the elastic moduli of very small or heterogeneous samples can be achieved. This method, called acoustic microscopy, was developed and tested for many years as cold and hot set-up; in 2011 an optimized version of the high frequency acoustic microscope has been definitively introduced in hot cell. This apparatus now constitutes a standard facility for irradiated fuels and materials characterization. This paper presents a review of the studies performed on different irradiated fuels in order to determine the elastic moduli. Behaviour laws are proposed in the burnup range up to ∼103 MWd kg−1. The results, supported by benchmarking the outcome of acoustic measurements with other characterization techniques, indicate that the elastic modulus of irradiated fuel can be assessed without preliminary knowledge of density. Thus with a single non-destructive measurement it is possible to assess both the density and the Young's modulus with an acceptable precision.